This invention relates generally to electrically powered fans, and particularly to ceiling fans.
There are several types of fans that are used within a room to circulate room air. These include portable fans that may be set up on the floor or on furniture, wall mounted fans, and ceiling fans. Portable fans and wall fans often oscillate. Whether or not they oscillate all three types of fans have a motor driven shaft to which an annular array of fan blades is mounted.
There are two principal types of electric motors used to rotate the blades of ceiling fans. The more popular type has a stationery stator mounted on an upright shaft. The rotor is rotatably mounted about the stator. This is known both as a direct drive motor and as an inside-out motor. The less popular type ceiling fan motor has the stationery stator surrounding the rotor that drives the fan blades.
Ceiling fans are mounted to ceilings with their motor rotors and stators oriented about vertical axes. So oriented, the bearings are subjected to axial loading from the dead weight of the fan system. That system includes the fan housing, rotor, blades, suspension system and any light kit. Ball bearings are typically employed which are designed for radial rather than axial loading. This serves to considerably limit the bearing life which results in imbalance and audible noise. To alleviate this problem thrust bearings have been used for axial loading which are totally submerged in oil to support the rotor. Although this serves to substantially enhance bearing life, and virtually to eliminate bearing-generated noise, such motors have still remained rather noisy. Moreover, the noise level of such has been erratic and inconsistent from one fan to the next.
Accordingly, it is seen that a need has long existed for a ceiling fan with good motor longevity and that is consistently quiet. It is to the provision of such that the present invention is primarily directed.
It has been found that the inconsistency and the excessiveness in the level of audible noise generated by ceiling fan operations arises primarily from inconsistence in the size and shape of the annular air gap between the rotor and stator of the fan motor. A new ceiling fan is substantially free of this problem. It comprises a housing adapted to be suspended from a ceiling. A shaft is mounted generally vertically in the housing with a cylindrical bearing surface located within the housing. An electric motor is mounted within the housing with its stator rigidly mounted to the shaft, it being adapted to be coupled with a source of electric power. The motor rotor is rotatably journaled about the shaft bearing surface radially about the stator. So constructed, the annular air gap between stator and rotor may be small for dynamoelectric efficiency and yet remain dimensionally consistent between manufactured lots even after packaging, shipment, installation and operation. This also results in consistently quiet fan operations.